physiology of grain yield in cereals, growth and maintenance respiration
TRANSCRIPT
ACHARYA N.G.RANGA AGRICULTURAL UNIVERSITY
DEPARTMENT OF AGRONOMY
112/28/15
Presented by:KANCHETI MRUNALINI
Physiology of grain yield in cereals
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In cereals, grain filling is largely dependent on photosynthesis and
environmental conditions after flowering, but the capacity for
storage is determined by conditions before flowering – have
dominant influence on yield.(Japanese IBP experiments on Rice P-
90).
In wheat, varieties in which the photosynthetic rate of flag leaves
under controlled environmental conditions falls substantially
during the period between end of stem growth and beginning of
grain growth, but rises again as export of assimilate to the grain
increases.
Seasonal sequence of condition plays a major role in determining
whether source/ sink is more limiting.
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In crop production point of view solar energy is to be
conserved for future use via its fixation is biomass by the
process of photosynthesis.
In this process, CO2 from the air is converted into
carbohydrates.
This Process is called CO2 assimilation.
6CO2 + 6H2O C6H12O6 + 6O2
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About 40% of weight of carbohydrates formed during assimilation process is lost by Respiration.Substraction of the rate respiration from the assimilation rates gives the rates of increase in plant dry weight
Part of the carbohydrates produced is used as building material
for structural plant drymatter as cellulose proteins lignin and
fats and a part of this as photosynthates used as a source of energy
for plant process.
The release of energy from carbohydrates produced during
assimilation process is described by the following equation.
C6H12O6 + 6O2 6CO2 + 6H2O + energy
This process is called respiration.12/28/15 5
Sigmoid curve of growth Sigmoid curve of growth raterate
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With respect to the growth rate 3 phase may be distribution :
During the first phase crop consists of individual plants that do not shade each other and crop growth rate, increases.
In the second phase crop covers soil completely and crop growth is constant .
In the 3rd phase crop is matured and crop growth rate is decreased .
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In the first phase major part of assimilates are invested in the leaf growth. This growth in leaf area is accompanied by a proportional increase in energy interception because neighbouring plants are so small that mutual shading hardly place a role.
Individual plant weight increases by constant proportion per day thus leading to exponential growth .
After a closed surface has been formed more leaf growth does not lead more light interception, hence the CG remains constant and total plant increase linearly.
In the last phase leaf senescence leads to decrease in the CG
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Major part of total drymatter accumulation is achieved during the second phase.
Total drymatter production of crop has largely determined by magnitude of CGR during linear phase and duration of the phase.
The duration of period of linear growth is superior and cultivar specific and more over is influenced by environmental conditions.
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Like solar radiation and temperature , supply of nutrients and water , occurance of weeds, pests and diseases , with an optimum supply of water and nutrients in absence of weeds, pests and diseases, the growth rate is determined by solar radiation and temperature and this is referred to as Potential Growth Rate.
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Assimilation in C3 and C4 cropsAssimilation in C3 and C4 cropsPhotosynthetic advantage of C4 compared with
plants at levels of carboxylation is attenuated at the whole leaf by combination of stomatal and mesophyll resistances and still more so at the level of crop photosynthesis by shading, periods of low light and respiration with the result that no consistent advantage of C4 pathway is evident in maximum crop growth rates and yields
.The real value of C4 pathway probably lies elsewhere
in its better adoption to high temperature –high insolation condition provided the nights are not cold, just as C3 plants perform better under cool conditions with only moderate insolation. 12/28/15 11
COCO22 assimilation of a single assimilation of a single leafleaf
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Maximum rate of net CO2 assimilation at high light intensity (Fm)
C4- plants – 30-90 kg / ha /hrC3-plants- 15-50 kg / ha /hrGrowth rate of respiration (Fg) is the sum of net
rate and the concurrent dark respiration.The dark respiration is at normal temperatures
roughly 1/9th of the maximum net assimilation rate .
Maximum net assimilation rate and dark respiration are much more effected by temperature than the initial light use efficiency.
Under field conditions , where plants are subjected to fluctuating temperature conditions, there appears to be adoption of the photosynthetic apparatus. 12/28/15 13
Canopy COCanopy CO22 assimilation assimilation For crop photosynthesis, relative advantage of C4 over C3 plants is
less than at the level of single leaf due shading of lower leaves and to increasing importance of aerodynamic compared with the leaf resistance to CO2 exchange(Slatyr, 1970)
Highest rates of photosynthesis measured on wheat crops (Denmead, 1970) by aerodynamic methods are only slightly less than those for maize.(Lemon, 1967)
If the crop is of C3 type LAI of one Assimilation rate is of 25 kg /ha /hr actual leaf area Ground areaFor an LAI of 4, CO2 assimilation rate is about 39 kg/ ha /hr12/28/15 14
Dry matter Dry matter AccumulationAccumulation
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Increasing light intensity and photosynthesis, increases demand for assimilates. (King et. al.,) can lead to increase in rate of assimilate export from leaves .
In rice grain filling is slow during low temperatures because of slow rate of translocation.(Murata and Matsushima)
Higher rates of mass transfer per unit phloem area is studied in Soybean petioles (Fisher, 1970) in leaves of C4 , grasses (Lush and Evans, 1978) and wheat roots (Passiouva, 1974)
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PartitioningPartitioning ofof AssimilatesAssimilates Pattern of assimilate distribution determined by rate
of photosynthesis, strength and proximities of various sink environmental conditions.
In sugarbeet, for eg., a limiting supply of photosynthates to leaves and more to roots instead under water stress.
Rice – flagleaf and penultimate leaves are main suppliers to ear.
(King et.al., )Pea, soybean, auxillary inflorescence supported by
subtending leaf. (Wardlaw, 1968)Cotton boll - younger leaf is responsible for yield.Root crops- uppermost leaves responsible.Older tobacco leaves preferentially support
younger ones 3, 5, 8 nodes above them. (Jones et.al., 1959)
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GROWTH AND MAINTENANCE RESPIRATION
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RESPIRATION
Oxidation of organic substances to CO2
and water
Can be divided into 3 groups :
Autotrophic respiration / plant
respiration.
Heterotrophic respiration / soil
respiration.
Photorespiration.
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AUTOTROPHIC RESPIRATION
o Capable of self-nourishment
o Requires only minerals for growth
o Uses carbonate or carbon dioxide as a source of
carbon and simple inorganic nitrogen as a
nitrogen source
Common chemical equation of autotrophic respiration for glucose is:
C6H12O6 + 6O2 6CO2 + 6H2O + energy12/28/15 20
The autotrophic respiration consists of:
•Growth Respiration
•Maintenance Respiration12/28/15 21
Diagram 2: Example of Autotrophic Respiration of plant12/28/15 22
GROWTH RESPIRATION
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Represents metabolic cost of converting the translocated
products of photosynthesis to structure,cytoplasmic/
storage .
The conversion of primary photosynthesis into structural plant
material as cellulase, proteins , lignin and fats requires and
energy for synthesis of end product , the transport of sugars
and the uptake of nitrogen and minerals.12/28/15 24
Therfore, part of the sugars assimilated is respired to
provide energy for the synthesis of new plant
components.
At higher temperature,rate of conversion of primary
photosynthates into structural plantmaterial changes but
the conversion efficiency remains constant, because the
biochemical pathway is not effected by temperature.
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MAINTIANANCE
RESPIRATION
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Maintenance respiration of crops towards end of their
life cycle, but it would be satisfactorily to base its
estimation as accordingly of non-storage protein and
membrane components which turns over for more
rapidly than all wall constituents and storage
polysaccharides, proteins and oils.
Proteins in the plant , especially in the leaves consist
mainly of enzymes which have only a limited life
span .
They deteriorate about 0.1% a day at a temperature
of 20 0
C and have to be resynthesized .
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Temperature is the most important environmental factor
affecting maintenance respiration
The metabolic costs of the repair of injury from stress
(biotic/abiotic) also considered as part of maintenance
respiration
Essential for biological health and growth of plants, sustain
living tissues.
Maintenance respiration is a key component of most
physiologically based mathematical models of plant growth,
including models of crop growth and yield and models of
ecosystem primary production and carbon balance.
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Maintenance versus growth respiration:
Growth respiration can be distinguished from maintenance respiration
by relating variation in respiration rate to variation in RGR over short
time intervals .
This approach assumes a model for respiration where:
{Total respiration} = {Maintenance respiration} + {(Specific costs of
growth} * {RGR)} ]
where respiration is expressed in mmol CO2 g-1
d-1
, and specific costs
of growth in mmol CO2 g-1
.
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Than
k you
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